MATERIAL/ ECO SPECIAL......................... Cellulose crystals as strong as steel

Cellulose crystals as strong as steel  Researchers may have discovered a new eco-friendly wonder material in the paper industry waste that could be used to strengthen construction materials and automotive components     The same tiny cellulose crystals that give trees and plants their high strength, light weight and resilience, have now been shown to have the stiffness of steel.Thenanocrystalsmightbeusedto create a new class of biomaterials with wide-ranging applications, such as strengthening construction materials and automotive components. Calculations using precise models based on the atomic structure of cellulose show the crystals have a stiffness of 206 gigapascals, which is comparable to steel, said Pablo Zavattieri, a Purdue University assistant professor of civil engineering. “Thisisamaterialthatisshowingreally amazing properties,” he said. “It is abundant, renewable and produced as waste in the paper industry.” The findings appear in the journal C ellulo s e. “It is very difficult to measure the properties of these crystals experimentally because they are really tiny,” Zavattieri said. “For the first time, we predicted their properties using quantum mechanics.” The nanocrystals are about 3 nanometers wide by 500 nanometers long – or about 1/1,000th the width of a grain of sand – making them too small tostudywithlightmicroscopesanddifficult to measure with laboratory instruments. The findings represent a milestone in understanding the fundamental mechanical behaviour of the cellulose nanocrystals. “It is also the first step towards a multiscale modeling approach to understand and predict the behaviour of individual crystals, the interaction between them, and their interaction with other materials,” Zavattieri said.     “This is important for the design of novel cellulose-based materials as other research groups are considering them for a huge variety of applications, ranging from electronics and medical devices to structural components for the automotive, civil and aerospace industries.”     The cellulose nanocrystals represent a potential green alternative to carbon nanotubes for reinforcing materials such as polymers and concrete. Applications for biomaterials made from the cellulose nanocrystals might include biodegradable plastic bags, textiles and wound dressings; flexible batteries; new drug-delivery tech; transparent flexible displays; special filters for water purification; new types of sensors; and computer memory.     Cellulose could come from a variety of biological sources including trees, plants, algae, ocean-dwelling organisms called tunicates, and bacteria thatcreateaprotectivewebofcellulose.     “With this in mind, cellulose nanomaterials are inherently renewable, sustainable, biodegradable and carbon-neutral like the sources from which they were extracted,” said Robert Moon, a researcher from the US Forest Service’s Forest Products Laboratory, who also authored the paper. “They have the potential to be processed at industrial-scale quantities and at low cost compared to other materials.”     Biomaterials manufacturing could be a natural extension of the paper and biofuels industries, using technology that is already well-established for cellulose-based materials.     “Some of the byproducts of the paper industry now go to making biofuels,sowecouldjustaddanotherprocess to use the leftover cellulose to make a composite material,” Moon said. “The cellulose crystals are more difficult to break down into sugars to make liquid fuel. So let’s make a product out of it, building on the existing infrastructure of the paper industry.”     The surface can be chemically modified to achieve different properties.     “For example, you might want to modify the surface so that it binds strongly with a reinforcing polymer to make a new type of tough composite material, or you might want to change the chemical characteristics so that it behaves differently with its environment,” Moon said.     Zavattieri plans to extend his research to study the properties of alphachitin, a material from the shells of organisms including lobsters, crabs, mollusks and insects. Alpha-chitin appears to have similar mechanical properties as cellulose. “This material is also abundant, renewable and waste of the food industry,” he said.

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